1. Field of the Invention
The present invention relates to wheelchair lifts or elevators and, more particularly, to combination stair and folding platform wheelchair lifts which translate from one configuration to the other depending upon the purpose to be served. Still more particularly, the present invention relates to an improved safety barrier/ramp actuating mechanism for said lifts and the method of operation thereof.
The improved safety barrier/ramp actuating mechanism of the present invention is especially adapted to wheelchair lifts having a safety barrier horizontally hinged to the bottom step of a combination stair and folding platform wheelchair lift wherein the bottom step in the stair configuration forms the outer panel of the platform configuration of the lift.
The invention includes a safety mechanism for preventing said barrier/ramp from actuating when the barrier is disposed as a ramp and a load is imposed thereon in excess of a preselected limit.
The present invention also relates to an improved method of operation of the various procedural steps which occur during the transformation of the wheelchair lift from a folding stair configuration to a platform configuration and during reconfiguring back to the folding stair configuration.
2. Description of the Prior Art
The art of combination folding stair and platform wheelchair lifts, which translate from one configuration to the other, depending upon the purpose to be served, is well-developed.
An example which illustrates the environment of the present invention is disclosed in U.S. patent Ser. No. 4,027,807 for a Wheelchair Lift, issued Jun. 7, 1977, to Graham R. Thorley. Thereshown is an elevator or lift for a wheelchair, or physically impaired person, which is particularly adapted to replace the entrance/exit stairs of a public transportation vehicle such as a bus, trolley, or light rail train car.
The Thorley '807 patent discloses a set of stairs having a lower step (A) which forms an outer panel of the lift when the stair/panel is transformed into a part of the lift platform (10) to operate as an elevator. The outer projecting end panel (50) of the platform serves as a ramp at the end of the platform and includes a safety flap (51) which flips upward from the panel to prevent a wheelchair from rolling off during vertical motion of the platform (Col. 2, lines 26-33). This safety barrier arrangement proved inadequate.
An improved version of the safety barrier/ramp combination end panel of the lift platform is disclosed in the patents of Donald B. Sullivan and Graham R. Thorley, the most recent of which was reissued May 28, 1991, as U.S. Pat. No. Re. 33,595 for Wheelchair Lift. The basic patent application was filed Sep. 27, 1982, and has issued as several different patents based on divisional and continuation-in-part applications. Therein disclosed is a wheelchair lift similar to the device of the Thorley '807 patent and which converts between a folding stair and raisable and lowerable platform configurations. The extended or outboard end of the platform configuration includes a panel which converts between a bottom step tread, a raisable safety barrier, and a wheelchair ramp.
Wheelchair lifts are presently made in the convertible stair/platform configuration for a specific purpose which is to be installed or retrofitted into the door system of a bus to permit wheelchair users to have access to public transportation as mandated by federal regulations. The wheelchair lift collapses into a stair configuration within the door system of a bus to permit use by fully mobile persons. However, once the doors are open, the stair configuration can be transformed first into a floor level platform by collapsing the stairs into a horizontal platform which projects outward from the bus so that it extends beyond the side thereof for a sufficient distance to extend over a curb. The stairs, upon flattening, are typically disposed at bus floor level which permits a wheelchair-bound or physically-impaired person inside the bus to roll or step onto the platform and then be lowered to the ground. Alternatively, upon extension, the platform can be lowered either to ground or curb level to permit a wheelchair or physically impaired person to be rolled or step thereon and then lifted to bus floor level for movement into the bus. The bus driver/wheelchair lift operator thereafter transforms the lift back into a stair configuration and the doors are closed.
Once the platform has been raised to bus floor level and the wheelchair moved into the bus, the lift operator selects the step configuration control. The barrier/ramp then retracts inward around the outboard end of the platform to lie flat on top of the outer panel of the platform during the transformation of the lift from platform to stair configuration at which time the barrier/ramp then serves the function as the tread of the bottom step of the stair configuration of the wheelchair lift.
These designs of the prior art have specific deficiencies which are capable of causing injury to passengers when there is a malfunction or they are operated incorrectly. The present invention overcomes these problems and provides a new and improved safety barrier/ramp actuating mechanism and an improved method of control for operating the combination folding stair and platform wheelchair lifts.